Yog comes to Earth on board a returning space probe which re-entered the atmosphere and crashed into the South Pacific Ocean. Yog traveled to Sergio Island and used his powers to possess and transform an oceanic cuttlefish, creating Gezora. Gezora rampaged around the island, causing havoc for its inhabitants and the J.S.D.F. until the people managed to lure Gezora into a field of flames, horrifically burning the creature and forcing it to retreat into the ocean. As Gezora began to die, Yog escaped, and possessed a lobster, forming Ganimes. Ganimes returned to the island, damaging the buildings by slamming into them with its claws, until it was destroyed by explosives. Yog escaped once more, and then divided his life force into another lobster and a rock turtle, forming another Ganimes and Kamoebas. Coordinating the efforts of both kaiju, Yog appeared to have control over the island until a swarm of bats flew out of a cave. With Yog now startled, his control over Ganimes and Kamoebas dissipated, and the two monsters clashed. Eventually, both monsters fell into a volcano, killing Yog for good.
Yog can possess creatures and turn them into giant monsters that follow his will. However, these monsters can escape Yog's control.
Yog can survive atmospheric entry with no injury.
One of the monsters controlled by Yog, Kamoebas, returns in Godzilla: Tokyo S.O.S. as a corpse that had died after Godzilla tore out his throat. Whether Kamoebas was under Yog's control, or if he was simply a lone member of his species is never explained, most likely due to the fact that most of the Millennium series doesn't follow the original Showa continuity. However, the "Kiryu saga" does in fact have many Showa films included in its continuity, so it begs the question of whether both Kamoebas are related.
In addition, given that Yog needed to be present for the original Kamoebas to be created, it is possible that a second Yog may have come to Earth, controlled a new Kamoebas, and was either killed when Kamoebas died, or escaped as he did when Gezora and the first Ganimes were killed.